Are you considering raising two or more littermate puppies? It may sound like a fun, heartwarming idea, but many experts would advise against it. That’s because it is said to lead to the so-called littermate syndrome (also known as littermate/sibling aggression).

We must underline this is a rather controversial topic because the syndrome isn’t scientifically proven. According to some, it’s only anecdotal and shouldn’t be an obstacle to placing two littermates into one loving home.

Keep reading to find out more and perhaps come to your own conclusion.

What Is Littermate Syndrome?

The term littermate syndrome refers to behavioral issues in puppy siblings or unrelated puppies of the same age raised in the same household beyond 8–10 weeks of age. 

The main consequence is that puppies tend to have trouble socializing with other dogs and/or humans and prefer each other’s company instead. One dog may also become notably more introverted than the other.

Also, when separated, they are both likely to become anxious and, in some cases, even aggressive. This littermate syndrome aggression may also be directed toward each other, especially if they are same-sex siblings. 

All of this also means that setting boundaries and training, essential parts of basic dog care, are likely to become much more challenging.

What Else You Need to Know

Now you know what puppy sibling syndrome is, but you probably have more questions, such as when it starts, how to avoid it, what scientists say, etc. For that reason, we dug a little deeper and gathered the following info.

At What Age Does Littermate Syndrome Start?

The syndrome typically starts at around 10 weeks of age. That age is approximately the best time to bring home a puppy, because their socialization period starts when they are 8–10 weeks old

If they are constantly together with a littermate during that period, they can develop an unhealthy attachment leading to the issues previously described.

How Common Is Littermate Syndrome?

There is no scientific data that provide an exact answer to this question or even an official diagnosis. That’s why some sources claim that dog sibling syndrome is a myth. However, many vets and dog owners have seen littermate puppies exhibit the negative behavior mentioned.

The closest answer we can give you is that the syndrome isn’t guaranteed, but it’s quite common according to everyday observations.

How to Prevent Littermate Syndrome

Considering everything we discussed so far, it’s fairly obvious that keeping littermates separate for a notable amount of time during the critical period is crucial. The activities during which they should be separated include:

  • Feeding
  • Walking
  • Training
  • Grooming
  • Playing with the owner
  • Sleeping

For instance, you can start by putting their individual crates close together, and gradually increase the distance between them. Also, each dog should be fed separately from its own bowl. 

Training sessions and playtime without the other sibling are essential to preventing littermate syndrome, because it allows each puppy to focus on you without any distractions. It also allows the puppies to bond with you individually, reducing the chance of behavioral issues even when they are together.

Additionally, it’s highly recommended to have each of the puppies meet other animals and people without their sibling in order to boost their socialization skills.

Keep in mind that just like us, dogs have different personalities, so different things will motivate them. This is another reason why you should spend time with each puppy separately — it would help you figure out what motivates each dog.

Can Littermate Syndrome Be Cured?

Fixing the syndrome is hard, but it isn’t impossible. Of course, the sooner you start the higher the chances of succeeding, so if you’ve noticed some of the potential symptoms, act immediately.

All the steps we just listed above should be followed, but if the puppies’ attachment is already super strong, you must do this gradually.

You should also consider consulting an animal behavioral specialist and getting professional help. After all, things can be difficult in the beginning even with one puppy, so don’t hesitate to ask for help.

Do Puppies Overcome Littermate Syndrome With Age?

Puppies don’t outgrow this behavior naturally. On the contrary, littermate syndrome in older dogs can get worse if you don’t try to prevent it earlier. This is why it’s crucial to react as soon as you notice the first symptoms.


What causes littermate syndrome?

The causes are not entirely clear, but some theories state that it may happen when the owners assume that two puppies can fulfill each other’s socialization needs, so they don’t spend enough time with them individually. 

Answering the question — “what is littermate syndrome?” — is easier than saying what causes it. What we do know for sure is that it’s essential to set aside time for training, playing, and walking your dogs separately while they are young and learning.

What are the symptoms of littermate syndrome?

The main symptoms are:

  • Fear of unknown people, animals, and places
  • Anxiety when separated from their sibling(s)
  • Difficulty with training
  • Crate issues
  • Refusing to eat alone

Are there any littermate syndrome studies?

There is no scientific evidence to prove this syndrome is real. However, we did find some information about an experiment organized by a guide dog organization.

It involved two groups of people — those in group one were given two puppies to raise while those in group two were given just one puppy. It’s important to note that the dogs were temperament-tested first. 

The results show that getting two puppies from the same litter always caused one of them to become temperamentally unsuitable for work, even if both started off as ideal candidates.

That being said, it’s important to mention that we don’t know whether the foster family had any experience raising two dogs at once and how much time they dedicated to working with them individually.

Can dogs recover from littermate syndrome?

If you notice the symptoms linked to littermate syndrome (especially if it’s earlier on), you can try to correct them. It takes lots of time and effort, but it isn’t impossible if you follow the suggestions we listed above.

How do you fix littermate syndrome?

The advice is to deal with the issue gradually by making sure your puppies experience various basic activities separately (eating, walking, training, and so forth).

Final Thoughts

If you’ve read our article carefully, you know that you, as a pet owner, should do everything you can to avoid dog littermate syndrome, even if its existence is still not certain. 

There are examples of littermates living together in harmony, but there are also numerous cases of what could be described as the syndrome. 

If you really want to have two dogs of the same age, perhaps the best thing you can do is wait at least 6 months to get the second one — or consider getting adult dogs.


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